Voice continuity between voice over internet protocol multimedia subsystem (VoIMS) over evolved universal terrestrial radio access network (EUTRAN) and general packet radio service enhanced data rates for global evolution radio access network (GERAN) circuit switched (CS) domain or UTRAN CS domain requires a transformation of a VoIMS session into CS voice and vice versa. This transformation falls into the voice call continuity (VCC) category, which is a feature of the third generation partnership project (3GPP) Rel-7. However, this Rel-7 feature requires “dual radio”, i.e., a simultaneous connection to the source and target radio during the transition period. The use of “dual radio” is possible between wireless local area network (WLAN) radio and GERAN, UTRAN or EUTRAN radio, but not possible between EUTRAN and GERAN CS or between EUTRAN and UTRAN CS.
There are several single radio (SR) VCC candidate solutions listed in 3GPP TR 23.882, such as (1) Combinational VCC (C-VCC); and (2) Inter-mobile switching centre (Inter-MSC) handover (HO).
Although not yet addressed, there is a need to achieve co-existence of single radio (SR) voice call continuity solutions with VoIP capable GERAN/UTRAN. The invention also provides a solution that achieves co-existence between the C-VCC solution and the inter-MSC HO solution. In case an operator has UTRAN or has started partial deployment of enhanced GERAN access that can support C-VCC, there is a need to interwork the two solutions by allowing using one or the other on per-call basis.